Radio antenna system



Jan. 29, 1946. G. T. ROYDEN 2,393,655

RADIO ANTENNA SYSTEM Filed Jan. 5, 1944 s sheets-sheet 1 INVENTOR 1650965 I fPOYDEN AGENT Jan. 29, 1946.

G-. T. R OYDEN RADIO ANTENNA SYSTEM Filed Jan. 5, 1944 3 Sheets-Sheet 2 l I I I l l I IN VEN TOR. GEO/P615 7T l-POYDf/V AGENT Jan. 29, 1946. G. T. ROYDEN RADIO ANTENNA SYSTEM 3 Sheets-Sheet 3 Filed Jan. 5, 1944 Patented Jan. 29, 1946 UNITED STATES TENT OFFICE RADIO ANTENNA SYSTEM Application January 5, 1944," Serial No. 517,001

14 Claims.

This invention relates to combination oscillation generator and antenna systems. More particularly, it relates to combinations of this sort in which the oscillation generator includes an electronic tube, suitably supplied from sources of energy and in which the antenna is of the rhombic type.

One purpose of my invention is to provide a combination oscillation generator and antenna, in which the electrical constants and properties of both these portions are mutually cooperative, so as to improve the frequency stability of such combination.

Another purpose of my invention is to utilize the energy ordinarily wasted in a terminating resistor placed at the farther end of an antenna of the rhombic type.

Still another object of my invention is to provide a combination oscillation generator and antenna, in which the energy ordinarily dissipated at the farther end of the antenna, is returned to the oscillation generating or amplifying portion of the system and there fed back into the system so as to increase the efiiciency thereof as a whole.

Yet another object of my invention is to provide, in a combination of the type just described, a feed-back action from the output to the input circuit of the electronic tube, via the antenna itself, a physical transmission line and an adjustable artificial line, so that the tube and associated circuits may constitute an oscillation generator.

A still further object of my invention is to provide a system of the type just described, in which the inherent feed-back action of the electrcnic generator through the inter-electrode capacities thereof is substantially eliminated, so that the feed-back action is obtained solely through the transmission and artificial lines connected to the antenna, thus affording a more complete control over such feed-back action and promoting frequency stability.

Yet another purpose of one form of my invention is to provide, in a combination generator and antenna system of the type just described, a circuit arrangement for withdrawing energy from the farther end of the rhombic antenna and to feed the input of the electronic tube with such energy, via circuits which are not sharply tuned, so that changing of the frequency radiated by the system may be readily accomplished by the employment of only a single main control, although additional provision for vernier control of the frequency may also be provided.

A still further object of my invention is to provide a relatively simple and compact form of radio transmission device which is of special utility in the military communication field. The system of my invention is particularly adapted for the emission of radio frequency energ over a comparatively broad band of frequencies, alternatively, without elaborate adjustments being necessary when changing from one frequency to another. Due to this particular feature, as well as to others, my system is very well adapted for the jamming of radio frequency signalling which it is desired to suppress, this purpose being accomplished by the emission of a radio frequency signal at substantially the same radio frequency which is being employed for carrying the signal to be suppressed.

Another object is to cause interference with enemy signals over a broad band of frequencies, while allowing desired communication on certain frequencies.

In the drawings hereunto appended, Fig. 1,

shows a form of my invention, in which a tuned anode circuit is coupled to a tuned grid circuit by a rhombic antenna and suitable transmission and artificial lines; Fig. 2, shows another form of my invention, in which other feed-back paths existing in the electronic tube itself, are neutralized; and Fig. 3, shows another form of my invention, in which the frequency is determined by a single main control and a single vernier control, while Fig. 4, shows a variant form producing interference over a wide frequency band for military purposes.

Fig. 5 shows yet another embodiment of my invention in the form of a combination transmitter and antenna, utilizing a transmitter of the master-oscillator power-amplifier type.

Referring now especially to Fig. 1, electronic tube l is shown as a triode, although other types of electronic tubes may be substituted in the circuits by such additional and alternative connections as will be apparent to one skilled in the art. The filament of tube 1 is shown as heated by battery 2, although it is to be understood that other suitable sources of cathode heating energy may be employed. The anode of tube I is supplied with energy from a source indicated for illustrative purposes by battery 3, it likewise being understood that any other source giving a current of suitable potential and character may be employed instead of this battery.

The grid of tube I is supplied with oscillatory energy from a tank circuit comprising inductor 4 and capacitor 5, connected as a parallel tuned resonant circuit, the frequency of this resonant circuit being adjusted to approximate the operating frequency at which the antenna portion of my system is to function. The cathode return of the grid is made from the lower end of the tank circuit just referred to, the upper end of the tank circuit being connected directly to the grid. The static potential of the grid is maintained at a suitable value by means of bias battery 'I connected in series with grid leak resistor 6 between the cathode and the lower end of the:

grid tank circuit 4, 5. A suitable by-pass capacitor 8 is connected so as to be in shunt with both resistor 6 and battery I, while the cathode. is grounded, as indicated, at I.

The anode energy from battery't, alsoshunted by a suitable by-pass condenser II, isfed to the anode through another tank circuit comprising inductor 9 and capacitor ID. This second or anode tank circuit is likewise adjusted so as to be substantially resonant at a frequency corresponding to that frequency which is to be radiated from the system as awhole.

In the remaining elements of the circuit, which are now to be described, certain portions perform a dual function, namely, the conveyance of energy from the output of tube I to an antenna and consequent radiative dissipation thereof from this antenna, and the conveyance of a certain portion of this energy back to the input circuit of tube I. This latter function constitutes a regenerative, or feed-back action; serving to maintain tube -I and its associated circuits in an oscillatory state. In the following description, it is assumed that oscillations already exist in the circuits connected to tube I, and the reason for the existence of such oscillation will be apparent after the following description of the feed-back mechanism employed.

The output, or anode tank circuit, 9, It, has coupled thereto an inductor I2, so that any oscillatory energy in this tank circuit may be withdrawn therefrom and transmitted via radio frequency transmission line I3 to the rhombic antenna M. It has been customary practice in the artto connect a terminating resistor to the farther end of such an antenna and the energy absorbed by suchresistor has been entirely dissipated, without aiding in any way either the operation of the generator feeding the antenna, or without directly contributing to the amount of energy radiated from the antenna. With the employment of my invention, the terminating resistor hitherto employed is omitted. In orderto prevent line reflection, or other unwanted effects, it is necessary that a certain amount of energy reaching the farther end of antenna I4 be removed from that particular point. With the circuits of my invention, there are included elements which withdraw energy from the farther end of antenna I4 and which likewise-transfer such withdrawn energy through suitable controlling means, and feed-back such withdrawn and controlled energy to the input circuit of the oscillation generator, 1. e. the grid circuit of tube I.

The special elements just described, which function to replace a terminating resistor, comprise a second radio frequency transmission line l5, extending from the farther point of antenna I4 backwardly to an artificial line I 5'. This artifieia1 line includes two inductors, I6 and I1, re-- spectively, which have mutual electro-magnetic coupling, as indicated by the arrow, andthe capacitor I 8. Inductors I6 and I1 each have one end connected to a common terminal I1, and capacitor I8 is shunted between this terminal and one side of transmission line I5. The other side 'of transmission line I5 is connected to the free end of inductor I6, so that the energy passing over line I5 is fed to inductor I6 and capacitor I8 in serie with one another. The free end of inductor I1 and the conductor of line I5, which is connected to capacitor I8, are respectively con nected to the two terminals of a feed-back inductor 2| by means of conductors 2 I. Feed-back inductor 2| is electro-magnetically coupled to input inductor 4 of the grid tank circuit, thus serving to feed tube I with regenerative energy.

The operation of the system shown in Fig. l somewhat resembles, with respect to the generation. of oscillations, the conventional feed-back type oscillator, employing electro-magnetic devices for securing regeneration. However, in the system of my invention, the feed-back energy supplied to the input grid circuit is not taken directly from any portion of the anode circuit, thereby avoiding the waste of any energy present in the anode output circuit. Instead of such direct feedback of energy, my invention utilizes for feedback purposes, the energy which would otherwise be wasted in a terminating resistor at the end or the rhombic antenna. The oscillatory energy appearing at the farther end of antenna I4, which normally would be dissipated at that point by a resistor, flows backwardly over line I5 and artificial line I5, so that it is ultimately fed to the input circuit of tube I via the coupling between inductors 2| and 4.

The frequency of oscillation of the system will be dependent, inter alia, upon the time required for the oscillatory energy to travel from the anode circuit through the transmission line I3, antenna I4, transmission line I5, artificial line I5 and feed-back path 2| to tank circuit 4, 5. Since each one of these recited element making up such feed-back path may be made stable with respect-to the oscillatory constants thereof, the frequency stability of the system as a whole, will be benefitted by an increase in the length of transmission line and an increase in the siz of the rhombic antenna. The primary or main adjustments controlling the frequency are made by means of capacitors 5 and Ii], located in the grid and anode circuits, respectively, for which reason these capacitors are indicated in the drawing as being of the variable type. However, it is to be understood that the resonant frequencies of both grid and anode tank circuits may be adjusted by other means. For example, capacitors 5 and It may be made of the fixed type and inductors and 9 may be made variable, for example, by the employment of so-called permeability tuning. A final or secondary adjustment of frequency may be made by adjusting the variable coupling between inductors I6 and II of artificial line I5. It is to be understood that such secondary adjustment is feasible only when it lies within the band of frequencies passed by the grid and anode tank circuits, respectively. The design of rhombic antenna I I, especially with regard to its employment at a predetermined frequency, is well-known in the art and by suitable design of this antenna the operating frequency may be varied over a comparatively wide range without sensible loss of efliciency, such variations being brought about by appropriate tuning of the two tank circuits and adjustment of artificial line I5.

In Fig. 2, there is illustrated a combination oscillation generator and antenna system, according to my invention, in which electronic tube I, constituting the oscillation generator, obtains itscathode and anode energy supplies in a manner identical with that shown in Fig. 1. Likewise, the output of oscillatory energy from the anode circuit is obtained via a tank circuit, also identical with that shown in Fig. 1. The rhombic antenna 14, fed by transmission line 13, is terminated by feed-back path [5, I and El, in a manner identical with that shown in Fig. 1.

The grid input circuit, in the embodiment illustrated in Fig. 2, is also biassed and by-passed, with respect to static potential and oscillatory currents, in a manner similar to that indicated in Fig. 1, but the upper end of bias resistor 6 is not connected directly to the lower end of inductor 4, but to an intermediate point of inductor 4. Two capacitors, 5 and 22, respectively, are

connected in series across inductor 4. The upper 7 7 end of inductor 4 is connected directly to the grid of tube I, while the lower end is connected, via neutralizing condenser 23, to the anode of tube I.

The method of connecting input circuit, cathode return grid coupling and anode reverse feed back, constitutes a neutralization circuit, as wellknown in the art, and detailed description of the functioning thereof is accordingly thought to be needless. The employment of such inter-capacitative neutralization, in connection with the other elements of my invention, allows the frequency determination and stability to be more completely dependent upon elements, such as the long transmission line l5, which are relatively more stable than the constants of electronic tube l. Therefore, this embodiment of my invention is especially useful where precision of frequency control is of great importance.

Referring now to Fig. 3, there is here illustrated an embodiment of my invention in which the number of controlling adjustments which must be made when the frequency is to be shifted, is reduced, thereby promoting simplicity and rapidity of frequency changing.

In Fig. 3, the oscillation generator, comprising electronic tube I, has the anode circuit thereof supplied with energy and delivering the oscillatory output in the same manner already described in connection with Fig. 1, i. e. via an antenna, transmission line and artificial line. The grid of tube I is directly grounded, with respect to oscillations, by means of by-pass capacitor 8, the suitable static operating potential being se cured by the use of bias battery 1 and grid leak resistor 6. It will be noted that in this embodiment, the common connection point between capacitor 8 and resistor 5 is connected directly to the grid, and not via the intermediary of any oscillatory circuit. The effect of inter-electrode grid-anode capacitance in causing undesired feed-back action within the tube itself is in this fashion avoided, so that the feed-back is obtained solely through the path l3, l4, l5, l5, 2|, as already described in connection with Fig. 2.

The cathode supply for tube I is secured from battery 2 via a network comprising capacitor 21, inductors 24 and 25, and capacitor 26. The cathode proper is, in this fashion, isolated with respect to oscillatory energy from the ground, so that feed-back energy may be applied to the cathode. This feed-back is provided by coupling coil 2|, receiving its energy in a manner similar to that described in connection with Fig. l, and coupled to inductors 24 and 25. The regenerative driving voltage is thus applied to tube I between the cathode and the grid, but at a point close to the cathode, which allows the virtual grounding of the grid, as above-mentioned.

In the employment of the embodiment shown in Fig. 3, adjustment of the variable element of anode tank circuit 9, ID, for example variable capacitor l9, serves as a primary adjustment for determining the frequency of a system as a whole. For final, or Vernier adjustment of the frequency, the mutual coupling between inductors I6 and I! may be varied, as already described in connection with Fig. 1.

It will be noted that inthe embodiment of my invention shown in Fig. 3, the energy which returns from the farther end of the rhombic antenna is fed to the cathode-ground circuit of the generating tube. Since the cathode-ground circuit is also a part of the anode output circuit and, since the energy so fed back has its current and voltage in phase with the current which re sults from the normal functioning of the vacuum tube, this energy will, at least in part, appear once again in the anode portion of the system, and from that point will be transferred again to the radiating portion of the system.

It can be seen, therefore, that the efficiency of a combination oscillation generator and antenna according to my invention, will be greatly increased by the utilization of such feed-back method, which utilizes energy hitherto inefficiently consumed by the terminating resistor at the farther end of the rhombic antenna. This increase of efficiency leads to the still further advantage that the power input fed to a given antenna from a given vacuum tube, may be made greater than would be obtained with the usual employment of a resistance terminated antenna.

One particular advantage of the embodiment of my invention shown in Fig. 3, is that it is capable of being shifted with comparatively great rapidity from one frequency to another, and that such shifting may be accomplished by the mechanical variation of a single tuning element. For example, the vario-coupler l6, l1 and the variable condenser l0, conveniently of the rotary type, may be kept in motion by any suitable means, such as a motor drive, whereby the emitted energy from a transmitter according to Fig. 3, will be continuously varied over a comparatively wide band of frequencies. One application of this property just mentioned, is the employment of such transmitter as a source of jamming energy, used in the military communication field for preventing or interfering with transmission of undesired radio frequency signals, produced by other transmitters. If the speed of variation of the vario-coupler I6, I! and condenser Ill be made comparatively rapid, there will be radiation over the entire band of frequencies covered, occurring at a rate sufliciently rapid to interfere with radio communication taking place anywhere within such band of frequencies. The necessary change of coupling between elements l6 and Il may be brought about by suitable mechanical means, synchronized with the device serving to rotate or otherwise change the value of capacitor H].

In Fig. 4, is shown a circuit operating in the same basic manner as that of Fig. 3 and illustrated with similar elements supplied with identical reference numerals. The grid and anode returns to the cathode are not, however, in this form made directly to the lower ends of inductors 24, 25, but a capacitor 28 is inserted between the lower ends of these inductors and the common grid-anode returns, joining at the point I. At 30, there is indicated schematically a moving contact driven from the same source which varies oapacitor l and theooupling of inductors l6 and 11, as indicated in the drawing by a dotted line. This moving contact sweeps over a stationary contact 3!, made, for example, in the form of an arc. At one spot, 32, this are is interrupted so that moving contact 36 will break the circuit when it passes over this gap 32. anode return is connected to stationary contact 3|, and movable contact30 is connected via resistor 2!! to the lower ends of inductors 24, 25.

It can be seen that if contact 33 is caused to rotate simultaneously with the rotation of condenser I3 and the variation of coupling of IE and H, the oscillatory circuits will be complete only aslong as contact 30 touches contact 3|, but will be interrupted when gap 32 is reached. Thus oscillatory energy will be transmitted over the band of frequencies covered by the rotation of condenser IS, with the exception of the frequency to which the oscillator is tuned when contact 30 reaches gap 32 If so desired, other gaps similar to that shown at 32, may be provided.

This form of my invention is particularly useful in military communication for purposes of jamming enemy communications over the band of frequencies covered by the oscillator, while at the same time allowing desired communications to be maintained at the frequency corresponding to gap 32. The use of capacitor 28 and resistor 29 avoids any undue sudden change in voltage and current,

which might otherwise occur when contact 3i: passes over gap 32.

Reference is now made to Fig. 5, where the tube feeding the antenna is shown associated with the same type of circuits and feed-back connections The common gridmonically related to the frequency exhibited by crystal 40, energy is withdrawn througha suitable tap 50, conveniently made adjustable, as here shown. This withdrawn energy passes through coupling condenser 44 to the cathode of tube l, which latter tube is excited by such energy and acts to amplify such energy, before delivering' it to the antenna, whence it is radiated.

Oscillations are supported in the circuit of tube 33, by reason of the feed-back which occurs through the stray capacitance between anode 39 and grid 38' of this tube. This stray capacitance is schematically represented in dotted lines by a capacitor 42.

It can be seen that the form of my invention shown in Fig. 5 operates in substantially the same manner as the forms previously described, but presents the advantage that the frequency may be better controlled, by reason of its derivation from a master oscillator, and permits the obtaining of higher output efficiencies, since all the energy fed back from the farther end of antenna l4, via transmission line l5 and associated elements, is utilized solely to be re-injected into the output system of amplifier tube 1. If this latter tube be properly chosen and designed, in a man ner familiar to one skilled in the art, very great efficiency of such feed-back action may be obtained without the production of self-oscillation in the circuits directly connected with tube i.

It can also be seen that a radio frequency amplifier having one or more stages may be employed in connection with the master oscillator and power amplifier as shown in Fig. 5 since the as in the case of Fig. 3. The various elements of the circuits associated with tube I bear reference numerals identical with those employed in connection with Fig. 3 and function in a substantially identical manner, with the exceptions hereinafter to be noted.

In this type of transmitter, the feed-back between inductor 2! and inductor 24, is made of insuflicient degree to cause tube I to act as a self-excited oscillator. Likewise for tube I there is chosen a type of tube which will function efficiently as a power amplifier. The oscillations are generated by tube 33 and its associated circuits, constitutin a master oscillator. This latter tube is here shown as a tetrode, but a triode or a pentode may be applied with such changes in the associated circuits as will be apparent to one skilled in the art. The filament of tube 33 is shown as heated by current derived from the battery 34, but it is to be understood that any other suitable source of power may be used at this point. Likewise the anode current for tube 33 is shown as derived from the same battery 3, which feeds the anode of tube I, through a suitable dropping resistor 35, by-passed by capacitor 36, it being understood that other suitable sources of anode energy may be employed in lieu of this battery. The screen grid 36 of tube 33, likewise may be kept at a suitable potential via dropping resistor 31, by-passed by capacitor 38 and fed via resistor 35 from battery 3. The control grid 38' of tube 33, is connected to frequency determining piezo electric crystal 40, shunted by a grid leak resistor 4!, one terminal of each of these. lastmentioned elements. being grounded.

The anode 39' of tube 33 is connected with the source of anode energy, supplied via inductor 39, shunted by variable capacitor 43. From the parallel tuned circuit constituted by the last two elements and adjusted to a resonant frequency harobjects of my invention may be attained with the input circuit of vacuum tube energized from any suitable source of radio frequency power.

It is readily seen by one skilled in the art that the artificial line may be omitted and the energy obtained from the far end of the rhombic antenna fed through the transmission line l5 directly to the input circuit of the vacuum tube l. Adjustment to the exact frequency desired could be made by changing the length of one of the transmission lines. Other ways of changing the effective length of the transmission line may be employed for the same'purpose such as by the use of short sections of lines connected to one of the transmission lines, by coupling an adjustable tuned circuit to one of the transmission lines, by inserting a dielectric material in the electric field between the conductors comprising the transmission line or placing a magnetic material where it will be magnetized by the current flowing through the transmission line.

There are other well known ways of transferring power from the anode to the transmission line than the inductor 9 and capacitor II). For example, a type of resonant circuit employing a transmission of line "short circuited at one end may be employed. The transmission line [3 may be coupled to this resonant transmission line or may be connected to it through blocking capacitors at such points as give proper impedance matching. Or a network may be used having more than one inductor or capacitor or a plurality of inductors and capacitors. 7

Other modifications, advantages and uses of my invention, beside, those above enumerated, will be apparent to those skilled in the art.

What I claim is:

1. Combination oscillation generator and antenna system including an electronic tube having a control grid, cathode and anode, means for supplying electrical energy thereto, a tuned anode circuit connected thereto, a rhombic antenna coupled to said anode circuit, an artificial line, a relatively long transmission line connecting said artificial line and the end of said rhombic antenna most remote from said anode circuit, and means coupling the output of said artificial line to the input grid circuit of said tube so as to sustain the oscillations generated by said system, said anode circuit, rhombic antenna, transmission line and artificial line being all adjusted so as efiiciently to transmit substantially the same frequency, so that energy in said anode circuit passes over the coupling to said antenna, from said remote end thereof over said transmission line to said artificial line and over said coupling means to said input grid circuit, and arrives thereat in oscillation-sustaining phase with respect to the energy already therein.

2. System according to claim 1, in which said input grid circuit comprises inductance and capacity so chosen that said circuit is resonant at said frequency.

3. System according to claim 1, including a grid return circuit to said cathode and in which said means for feeding the output of said artificial line to said input grid circuit are located at a point close to the grid cathode return of said tube and including a direct radio frequency ground connection to said grid, whereby undesired feed-back of electrical energy through the inter-electrode tube capacities of said tube is substantially eliminated.

4. System, according to claim 1, also including a neutralization circuit connected between grid and anode of said tube, whereby feed-back is con-. fined substantially wholly to the path including said antenna, transmission line, and artificial line.

5. Combination oscillation generator and antenna system including an electronic tube generator having a cathode, grid and anode, a cathode heating source, inductors isolating the oathode from said source with respect to oscillations, an anode energy source, a tuned circuit connected between said anode energy source and the anode, a path of low impedance at radio frequencies between the grid and the end of the inductors adjacent to the cathode heating source so as to prevent inter-electrode coupling, a rhombic antenna coupled at the near and to said anode tuned circuit, a transmission line of matching impedance aperiodically connected to the farther end of said antenna so as to withdraw energy therefrom, an artificial line of matching impedance aperiodically connected to said transmission line and fed thereby, and relatively untuned means coupling the output of said artificial line to said cathode isolation inductors, whereby the tuning of said anode circuit and the tuning of said artificial line suffices to determine the oscillation frequency of the system as a whole.

6. Combination oscillation generator and antenna system including an electronic tube generator having a cathode, grid and anode, a cathode heating source, inductors isolating the cathode from said source with respect to oscillations, an anode energy source, a tuned circuit connected between said anode source and the anode, a path of low impedance at radio frequencies between the grid and the end of the inductors adjacent to the cathode heating source so as to eliminate inter-electrode coupling, a rhombic antenna coupled to said anode tuned circuit, a transmission line connected to the farther end of said antenna and withdrawing energy therefrom, an artificial line connected to said transmission line and fed thereby, and relative untuned means coupling the output of said artificial line to said cathode isolation inductors, wherepy the tuning of said anode circuit and the tuning of said artificial line is sufficient to determine the oscillation frequency of the system, said system also including means for substantially continuously varying the tuning of said anode circuit and said artificial line over a predetermined relatively wide band of frequencies, while keeping said frequencies substantially in agreement, so as to cause interference radiation over said band, and means for interrupting the generation of oscillations each time said tuning reaches a predetermined relatively narrow band of frequencies, whereby interference radiation at said predetermined narrow band of frequencies is suppressed.

7. System according to claim 6, in which said generation interrupting means includes a capacitor capable of passing the generated oscillations therethrough and includes a resistor normally connected in parallel with said capacitor and in series between the cathode and the common grid-anode return to said cathode, a normally closed interrupter functioning to determine the opening and closing of the circuit of said resistor, and means for moving said interrupter in synchronism with the variation of tuning of said anode circuit and said artificial line, whereby said interrupter opens the circuit of said resistor only when said tuning lies within said predetermined relatively narrow band of frequencies.

8. Combination oscillation generator and antenna system according to claim 6, in which said means coupling the output of said artificial line to said cathode isolation inductors is so adjusted as to afford an insufficient degree of coupling to produce self-oscillation of the portion of the system including said antenna, said system also including a master-oscillator, means for feeding energy thereto, means for determining the frequency thereof, and means for coupling the oscillations produced thereby to the first described electronic tube, said electronic tube thereby functioning as a power amplifier and the energy fed back by said artificial line being at least in part fed again to said antenna, whereby greater efficiency is secured.

9. A radio transmitter comprising a rhombic antenna. an electronic tube having a cathode, an anode, and a control grid, means for supplying electrical energy to said tube, an anode-cathode circuit and a grid-cathode circuit fo said tube, and a feed-back circuit between said anode-cathode and grid-cathode circuits including the conductors of said rhombic antenna.

10. A radio transmitter comprising a rhombic antenna, an electronic tube having a cathode, an anode and a control grid, means for supplying electrical energy to said tube, an anode-cathode circuit and a grid-cathode circuit for said tube, means for coupling one end of said rhombic antenna to one of said circuits and means for coupling the other end of said rhombic antenna to the other of said circuits, whereby said antenna is included in a feedback circuit for said tube.

11. A radio transmitter comprising a rhombic antenna, an electronic tube having a cathode, an anode and a control electrode, means for supplying electrical energy to said tube, an anode-cathode oircuit and a control electrode-cathode circuit for said tube, means for coupling said anodeing electrical energy to said. tube, an anode-oathv ode circuit and a, control electrodev-cathode 'cir q t er d, u e m an c edi t e'e d' of the two converging conductors atone yertex of said 'rhompic antenna, for coupling said antenna to said anode cathoqe circuit and means coniri ecteq to the ends of the two converging conductors atthe opposite yertex ofggid antenna for coupling said. antenna. to said control electrade-cathode circuit.

) 13. A radio transmitter comprising {i nombic antenna, an electronic tqbe havin'g a. 'cethorle, an anode and a control electrode, meang for supplying electrical energy to said tube, ananode-cathgo the u se ful-outputof'said tube.

GEORGE T. RQYDE'N. 

